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  No doubt aware of this, a forward-thinking young aristocrat named Pilâtre de Rozier, already well known in Parisian society for his scientific demonstrations, insisted on himself instead. On the initial tentative flights he rose just above the trees and rooftops, stoking a fire of straw and chopped wool in a hot-air balloon that, however, remained roped to the ground. Such tethered flights were, of course, too timid to justify much excitement. For the far more ambitious step of true free flight, de Rozier enlisted another young aristocrat to serve as ballast and companion and to help stoke the fire. He was a cavalry officer named the Marquis d’Arlandes, a friend of a friend of Marie Antoinette. These two – Pilâtre de Rozier and the Marquis d’Arlandes – became on November 21, 1783, the first of our species to break free of the ground. They took off before huge crowds in the Bois de Boulogne, drifted over Paris for twenty-five minutes, and after a trip of about five miles, having crossed the river Seine, landed near the present Place d’Italie.

  Though the flight was a success, the big Montgolfier balloon suffered from a serious flaw: Its envelope was made of canvas and paper and had a dangerous tendency at its base to ignite in flight. The two airmen carried a bucket of water and extinguished the life-threatening flames with wet sponges. They did this casually by today’s standards, and floated over the city as if in a dream. If the marquis’ written account of the flight was admirable for its tone of Gallic nonchalance, it became heroic two years later when Pilâtre de Rozier was burned and killed in a balloon of his own design, becoming not only the first man to climb free of the earth but also the first man to die for it.

  This was less important than it seemed at the time. By modern standards ballooning turned out to be a limited and impractical pursuit – not the sort of act that could take people where they wanted to go. As a result, though the first feeble moves away from the ground remain a curiousity, they lack the intellectual content that can sustain our interest now. Nonetheless, one unexpected and apparently simple observation of the human landscape still emerges from the marquis’ account to lead us farther into our sky.

  Naïvely, he wrote, ‘I was surprised at the silence and the absence of movement which our departure caused among the spectators.’

  What interests me here is the likelihood that the Marquis d’Arlandes was wrong. Parisian crowds are hard to impress and harder still to silence, as Louis XVI discovered a few years later. But solitary observers can be self-centered creatures, innocently assuming that others enjoy the satisfaction of their own full bellies. The marquis, it seems, had been disoriented by his sudden separation from the earth. I wonder: In his confusion did he attribute to the crowds what he himself felt – the sudden peace within the gondola, the eerie smoothness of balloon flight, its windlessness in the wind?

  That sort of transposition remains today the most common illusion in the experience of flying. People on the ground know milder versions of similar reversals, observing, for example, that the sun moves toward the west, when of course it is the ground that moves toward the east. But above that, deep inside the sky, the confusion is heightened by flight’s strange motions and by its utter detachment from the earth. The full extent of that detachment takes years to understand and accept. Until then balloonists continue to have the impression during takeoff not that they are climbing but that the ground crew, faces upturned, is sinking away. Airplane passengers have the impression that they are holding still, suspended in space as, far below, a miniature nation slides by. When they overtake a slower airplane they say it seems to come swimming by them backward. When another airplane passes head-on in the opposite direction they comment on its startling speed. When they fly through billowing clouds they speak of the inevitability of head winds. And when in order to turn they bank to one side, expecting to feel the tilt, they find instead that the world outside has toppled in the opposite direction.

  I was reminded of this one day while riding in the back of a Boeing 737 departing from San Francisco on a short flight down the coast to Los Angeles. The morning was bright. We swept up the San Francisco Bay in a gently banked left turn along the city’s waterfront, out toward the Pacific. Despite the airplane’s bank, most passengers peered through the windows, cautiously admiring the view. But the pilots were too enthusiastic. Directly over the Golden Gate, they rolled suddenly into a steep turn, dropping the left wing so far below the horizon that it appeared to pivot around the bridge’s nearest tower. I imagine they thought of the maneuver in technical terms: We were turning already, and for just a few seconds we would exceed the airline maximum of a thirty-degree bank. The maximum is aerodynamically unimportant at cruising speeds and is imposed only for peace of mind. Sightseeing seemed more important now. The pilots probably figured they had done us a favor.

  But they had not. As the airplane pivoted, the startled passengers looked away from the windows and met the eyes of their unhappy neighbors. A collective gasp rippled through the cabin. The reaction did not surprise me. Over the years I have learned never to bank steeply with my own passengers without first preparing them for the maneuver, and have noticed that even then many of them become helpless and disoriented. I do not blame them, either. As an instructor of experienced pilots, I have heard gasps and worse from my students. Pilots are merely well-trained passengers. They have to be reminded not to flinch, whimper, or make audible appeals to the Savior. They have to be encouraged to ride the airplane willingly, from the inside, and to think as it thinks. And they have to be convinced of the strange logic of the turn. At its center lies the peculiar relationship between the bank and the resulting movement of the airplane and the fact that neither can be felt. Such nothingness is what the passengers sensed when the airplane tilted over the Golden Gate – like the Marquis d’Arlandes’ windlessness in the wind, an eerie lack of feeling where feeling should be.

  Indeed lack of feeling associated with the bank is so disorienting, so unlike experience on the ground, that many people refuse to accept it – even after they have had the turn carefully demonstrated to them. This is because they may feel the lurch as the airplane dips its wing, starting into a turn or starting out of it, and they allow this to fool them into believing that they can feel the bank itself. When the bank is visible, they ascribe their unease to fears that the airplane might slip to the side, or capsize, or somehow tumble. When the bank is not visible, during flight inside the clouds or on black nights, they no longer worry because, in their minds, that which cannot be felt does not exist.

  Over history, pilots have made the same mistake. The airplane is such a simple device. Certainly the wing’s profile is one of nature’s purest forms. And our species was given its use before anyone knew even its most basic characteristics. Pilots as a result had to go about teaching themselves to fly. It took several generations. Eventually they had to admit that instinct abandoned them in the clouds and that they needed special instruments to tell of the bank. Without the instruments, they went into mysterious and uncontrollable turns and sometimes died. With the instruments, they maintained control and survived. Thus was born the most basic distinction in flying, between conditions in which the turn is visible and conditions in which it must be measured. And since the ability to fly through the weather has proved to be more important than speed in the conquest of distance, the mastery of the turn is the story of our sky.

  The bank is a condition of tilted wings, and the turn is the change in the direction which results. The connection between the two is inexorable: The airplane must bank to turn, and when it is banked it must turn. The reason is simple. In wings-level flight, the lifting force of the wings is directed straight up, and the airplane does not turn; in a bank, the lifting force is tilted to the side, and the airplane therefore must move to that side. It cannot slide sideways through the air because it has a vertical fin on the tail, which forces the turn by keeping the tail in line behind the nose. The result is an elegantly curved flight path, created as the airplane lifts itself through the changes in direction.

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bsp; The miraculous part of the maneuver is that the turn has an important balancing effect on the bank that causes it. The same effect, in cruder form, steadies cars on banked roadways, and bobsleds on the vertical walls of icy tracks. The difference in airplanes is that as the bank angle increases, the turn also quickens and by doing so automatically delivers a balance that is perfect. Bicycles react similarly: When they start to topple, they turn and thereby keep themselves up. Airplanes are even steadier. They operate in three-dimensional space and do not rely on tires to keep from sliding to the side. They will never capsize, no matter how steeply they are banked.

  Consider for contrast the primitive banking or ‘heeling’ of a sailboat, which does not cause a turn and which amounts to a simple trick of balancing the forces of the sail against those of the boat’s ballast – whether a heavy keel or some other form of counterweight. The magnificent sensation of speed it gives is all froth and spray. The truth is, heeling slows most boats. Racers accept it as an unfortunate byproduct of the conflicting forces that allow the boat to proceed upwind. Passengers do not enjoy it in boats any more than in airplanes, but they understand it better: Heeling a boat is a thrill seeker’s gambit; if it goes too far, the boat will capsize and perhaps fill with water; if people don’t brace themselves, they will slide across the deck and slip into the waves. It is ironic that the physics intend boats to move on level bottoms, but require of airplanes the banked turn.

  It is true that as the bank steepens in flight, directing more of the wings’ lifting force into the turn, the airplane has greater difficulty holding its altitude. Flown at bank angles approaching ninety degrees – in which the wings point straight up and down – no normal airplane can keep from descending. (Some fighters can, but only because at high speeds the fuselage itself creates lift and becomes a wing.) In such ‘knife-edge’ flight the wings exert all their lifting force in a direction parallel to the earth’s surface, and gravity pulls the airplane down. But if the pilot controls the airplane carefully and allows it to keep turning, it will happily roll past the vertical, onto its back, and finally right side up again. During such a maneuver, San Francisco Bay momentarily appears above you, and the Golden Gate Bridge seems to hang from the water. This is fine, if you are prepared for it. Full rolls are the purest expression of flight. They are normally flown only in fighters and other acrobatic airplanes, but if you ignore convention you can safely fly them in any airplane, including a Boeing 737.

  None of this would have comforted the man sitting next to me during that steep turn over the Golden Gate. He was large, sharp-eyed, and very alert. When the wing dropped, he said, ‘Hey!’ and grabbed the armrests. Now he rode ‘above’ me in the bank, leaning into the aisle as if he feared he might topple into my lap. He need not have worried. If he had dropped his pen, it would not have fallen ‘down’ in the conventional sense – toward me and the earth – but rather toward the tilted carpet at his feet. If he had dangled the pen from a string, it would have hung toward the floor.

  A dangled pen is a primitive inclinometer, like a plumb bob or the heel-meter of a sailboat. On land or at sea, it hangs toward the center of the planet. But in flight, it hangs toward the floor, no matter how steeply the airplane is banked. A carpenter’s level would be equally fooled. This peculiar phenomenon is another manifestation of the turn’s inherent balance. The earth’s gravity acts normally on an airplane, but so do the forces of inertia. Inertia is the desire of any mass to keep doing what it has been doing – in an airplane, to keep moving, and moving straight. During a turn, inertia pulls horizontally. In cars, it causes people to skid off roads. In airplanes, it combines with the downward force of gravity to create a new force that pulls constantly toward the floor. Actually, the force pulls toward points in space, but by banking, the airplane places its floor directly in the way – it has to, in order to turn. The neatness of this Newtonian package is beautiful to behold. Bob Hoover, a legendary stunt pilot, used to set an empty glass on his airplane’s instrument panel and pour himself a drink while flying full rolls. Our 737 pilots seemed inclined to fly the same way. If they had, as we passed through the inverted position and saw the Golden Gate Bridge hanging from the water, my sharp-eyed neighbor could have watched his pen dangling toward the sky. The flight attendants could have walked upside down. And some passengers, too self-occupied to look outside, would not have even noticed.

  The human body is just another inclinometer. Undisturbed by the view, it sits quietly in its seat, dangling its feet toward the tilted floor, churning out reports for the home office. This is difficult to accept about ourselves. The inner ear, and with it any useful sense of balance, is neutralized by the motion of flight. It is our greatest weakness as fliers that, having acquired wings, we still lack an instinctive sense of bank.

  For passengers this actually offers certain immediate advantages. The man next to me, for instance, was not about to fall into my lap. He could have relaxed, lowered the tray in front of him, and called for a coffee. Unlike the table in a sailboat, an airplane tray requires no gimbals. Flight attendants brew coffee on fixed counters, deliver it without worrying about the airplane’s bank angle, and fill cups to their brims. Full cups make people behave during turns: if they try to hold them level with the earth, the coffee pours out and scalds their thighs. If this seems unusual, imagine the alternative, an airplane in which ‘down’ was always toward the ground. Bedlam would break loose in the cabin during every turn. Unless people held their coffee just right, they would scald their neighbor’s thighs.

  Better to leave physics alone. As it is, as long as you contain your curiosity about what is happening outside, the inside of the cabin remains a steady and unsurprising little world. The turbulence which causes an airplane to shudder and buck is less important than people imagine. After hours on their feet, flight attendants do not develop sea legs. Passengers need no encouragement to stand and walk about. If he had stopped leaning, my neighbor could have stood up and danced the length of the tilted aisle.

  The situation is not quite so carefree up front in the cockpit. In fact, the forces which tame the cabin during turns are the very same forces which over time have provided pilots with the most deadly problem of flight control. As long as its wings are level, the airplane is by nature a well-mannered animal, and slow to anger. If you pull its nose up, then release the controls, it puts its nose back down; if you push its nose down, it answers by rearing back up. Like horseback riding, flying consists mostly of leaving the beast alone, allowing it to do its own thinking. The problem is that this particular beast does not stay on the trail unguided. And once it strays, it develops a strong impulse to self-destruct.

  Unguided, any airplane will eventually begin to bank. That in itself is fine if you don’t mind the resulting turn, meaning the change in direction. But as the bank tilts the lift force of the wings, reducing their vertical effectiveness, it erodes the equilibrium that previously countered the pull of the earth. The airplane responds to the loss by lowering its nose and accelerating. Sitting in the cockpit with folded arms and watching it proceed is like sitting on a temperamental horse and letting it gallop down a steepening slope: It requires a morbid curiosity and steady nerves. In flight, the slope steepens because the acceleration tightens the airplane’s turn, which increases its bank angle, which causes further acceleration. A sort of aerodynamic lock-in occurs. The airplane banks to the vertical or beyond and points its nose straight down.

  That is the spiral dive. In its most virulent form pilots sometimes call it the graveyard spiral. The airplane descends in ever steeper circles and either disintegrates in mid-air from the air pressures of excessive speed or shatters against the ground at the bottom of a screaming descent. All flights would suffer this end if the pilot (or autopilot) did not intervene.

  In good weather the intervention is easy. You hold the controls lightly, and when you see that the airplane has banked, you unbank it. During turns you hold the controls more firmly and keep the nose from dropp
ing. The increased loading created by inertia during such a well-flown turn is felt within the airplane as a peculiar heaviness – a ‘pull’ not toward the ground, of course, but toward the cabin floor. Pilots measure it in ‘Gs,’ as a multiple of gravity’s normal pull on the surface of the earth, or in steady wings-level flight. An airplane that banks to thirty degrees, the airline standard, creates a loading of 1.15 Gs: The airplane, and everything in it, temporarily weighs fifteen percent more than normal. Fifteen percent is just barely noticeable. But only a bit steeper, at a forty-five-degree bank, the load increases to 1.4 Gs: People feel pressed into their seats, and if they look outside they may notice that the wings have flexed upward. Technically, such loadings are not important. Airplanes are strong and flexible, and pilots shrug off 2 Gs and may feel comfortable at twice as much. But passengers are unaccustomed to the sensation. As we pivoted over the Golden Gate, the man in the seat beside me suddenly gained about eighty pounds. Had he dangled his pen toward the tilted floor, it would have pulled on the string with surprising force. This might not have reassured him. But the extra heaviness was a measure of the pilot’s success in resisting the spiral dive. If we had felt ‘normal’ during the turn, it could only have meant that the nose was dropping fast toward the water.

  No pilot would make such a mistake on a clear day. The view from the cockpit is dominated by the horizon, the constantly renewing division between the sky and the earth. It forms a line across the windshield and makes immediate sense of the airplane’s movements. Birds, too, use the horizon. The sight of an angled and shifting world must act powerfully on them. They are subject to the same laws of physics as airplanes, but they fly with insouciance, neither worrying about their inability to feel the bank nor pondering the explosive nature of the spiral dive. They can get away with this not because they are better fliers than we – in truth, they are worse – but because they can wait out bad weather and usually do. People do not have that luxury. We fly on schedules, through clouds and storms and across the blackest nights. When no useful horizon is visible outside the cockpit we maintain control of the airplane by reference to an artificial horizon on the instrument panel. And so we outdo the birds.